This invention relates to a radar apparatus with an inclined slot wave guide array to form a narrow azimuth beam and a dielectric lens in front of the array to form a narrow elevation beam.
The present construction is directed towards a motor vehicular collision warning system which includes a scanned beam sensor, a signal processor, and a vehicle interface system that initiates warnings to the driver or adaptively controls the vehicle. In this forward looking collision warning system, the sensor is designed to project a narrow beam of energy toward objects in the forward field of view. A forward collision warning control of this type for a vehicle can require a unit life in excess of two hundred million cycles at extreme temperatures. Thus, reliability requirements are high and unit costs must be low.
It is known that transfer slots in the narrow wall of a rectangular wave guide do not normally radiate when energy is propagated through the wave guide. In order to obtain radiation from a transfer slot in the narrow wall of a rectangular wave guide, it is necessary to incline the slot from the transverse position so that a component of the current is transversed to the narrow dimension of the slot. For an environment such as a motor vehicular collision warning system, the dimensions of a rectangular wave guide for a millimeter wave band are quite small. Thus, a problem is presented in using a narrow wall wave guide with inclined slots in a compact area such as exists in a motor vehicular collision warning system.
Since an antenna for a vehicle collision warning system must be small and lightweight to simplify the scanning mechanism, several known antenna constructions are not suitable, including reflector type antennas with fixed or moving feeds, planar wave guide arrays, and microstrip or stripline arrays. Further, the antenna should not be resonant so that its tuning is not critical or frequency sensitive. Moreover, the transmission losses in the antenna should be minimized.
Another issue with respect to any antenna for a vehicular collision avoidance system is whether the antenna can provide a beam suitable for processing. A collision warning system for a vehicle requires that the antenna be capable of millions of cycles at extreme temperature ranges. Thus, to provide an antenna that is compact and readily scannable with low transmission losses is a substantial challenge.
Therefore, it is an object of the present invention to provide a non-resonant, compact, and low loss antenna structure for use with a vehicular collision warning system.
In accordance with this invention, a radar apparatus is provided with a rotatable antenna structure such as a slotted wave guide antenna. The antenna is driven to oscillate back and forth at a small angle. A transceiver is coupled to the antenna and the antenna passes transmitted and reflected radar signals to and from a target as it is oscillated back and forth. The scanned signals are directed to a processor and then to a vehicle interface system for initiating warnings to the driver or adaptively controlling the vehicle.
The rotatable antenna is mounted to a tuned mass and spring scanner assembly which is designed to produce a controlled harmonic oscillation at a specific resonance frequency when excited by a chain of timed electrical impulses. The impulse timing, duration and amplitude are based upon feedback provided by a position sensor on the scanner.
The antenna of the present invention includes a narrow wall, inclined slot wave guide array for forming a narrow azimuth (horizontal) beam. A dielectric lens is placed in front of the array to form a narrow elevation (vertical) beam. The line array of the antenna is non-resonant. Further, the combination of the inclined slot wave guide array and dielectric lens allows for the formation of horizontal and vertical patterns which may be readily scannable. Moreover, the arrangement is compact and has minimal transmission losses.
The antenna and lens arrangement is used with a millimeter wave vehicle collision warning radar system. The antenna rapidly scans the area in front of a vehicle for providing a narrow beam radiation pattern. Since only the small and lightweight wave guide is moved for scanning, it is possible to rapidly scan the antenna beam with a very low power mechanism.
The foregoing and other advantages and features of the invention will be more apparent from the following description when taken in connection with the accompanying drawings.